SamsungExynos4RIL: Allow signal strength to be handled for GB modems

For devices that have no modems that support the ICS signal strength handling, allow handling it the old way with the ro.ril.gbmodem system property.

Change-Id: I68270c5a4026b2c8f448125607ee47dd04249176
Merge remote-tracking branch 'upstream/cm-10.1' into cm-10.1